DC Desalination - The pitch

Waste heat means wasted opportunity. DC desalination could make tens of billions of dollars in profit per DC in water scarce cities.

DC Desalination - The fun part

What I like about this idea is how it uses what would normally be considered waste to add value, billions of dollars of it. Designing a MED that would be very efficient and not require much O&M would be important. The design would also require that the MED handle the fluctuations in load the come with data centers.

DC Desalination - The growth potential

If this was done in LA it could make $80 to 90 billion a year in profit. There are probably five to ten other cities where this would make sense. The global profit could be close a trillion dollars.

DC Desalination - The monetization

The goal would be to convince one of these tech companies to build a DC in one of these water poor regions; DC Desal would then pay the tech company for their waste heat. For an idea how how much this might be worth, lets take a look at Los Angeles. In the dry season, the cost of water is basically $4 per hundred cubic feet or $1.40 per cubic meter. Using electricity for an MED plant, it’s possible to achieve $0.70 per cubic meter of desalinated water, or half of what LA citizens are paying. It’s worth noting that the water cost they are paying is likely heavily subsidized or politically negotiated with other parts of the state. Now, if the company running the DC is paid $0.40 for the heat required to desalinate a cubic meter of water and the water was sold to the city at the current rate, that would be a dollar of profit per cubic meter.

The electricity cost in LA is about $0.20 per kilowatt hour. It takes roughly 3.5 kWh to make a cubic meter of water using MED. Let’s say that the DC that would be built would have an average load of 40 megawatts and 35 of those would turn into heat used for desalination. That means that 240,000 cubic meters (or 63 million gallons) of drinking water could be produced per day. The per capita daily usage of water in LA is 123 gallons, so this could be enough water for about half a million people or an eighth of the city’s population. If revenue from the water is $1 per cubic meter, that would be $88 billion a year. The cost of building the MED would be several hundred million to half a billion dollars, which could be paid for within two days of desalination revenue.

Another, smaller, source of revenue would be the sea salt from the brackish water that comes out of the MED. Ocean water has 35 ppt salt or 35 kilograms per cubic meter of water. The brackish water wouldn’t be pure salt water, but that’s good enough for this approximation. Per day that would be 8,400 kg of sea salt. I think the salt would be worth about $2 per kg. Over a year there would be about $6 million for salt. Clearly the salt isn’t nearly as valuable as the clean water.

DC Desalination - The idea

There are many corners of the world that have access to abundant seawater but where potable water is expensive. Some of those places are also affluent like the cities of Los Angeles and San Diego in California and several cities in the Middle East and southeast Asia. The key to this idea is to find a way of doing desalination that doesn’t require getting the salt water warmer than 80 degrees centigrade because data center processors have a much shorter lifespan above that temperature. That temperature rules out boiling the seawater as well as concentrating it over a series of flash boilers. Thankfully, there is a solution, and that is Multi-effect distillation (MED). Instead of just evaporating water and letting it go into the atmosphere, MED captures the pure water in the form of steam and condenses the drinking water back into its liquid form (while heating up more saltwater). Most MEDs are typically run below 70° C, so we don’t need to worry about overheating the processors. If you know some thermodynamics, MED may sound like magic. If you take room temperature salt water and boil it to get pure water steam, it requires a lot of energy and the heat source must be above 100° C. One of the keys to MED is that the final product that you want is room temperature drinking water, not steam. So, you can use the heat from the steam to heat more saltwater. Theoretically, the only energy lost is from the differential heat of vaporization between pure water and salt water and the pumping energy, which isn’t much compared to the heat of vaporization. It’s possible to be ten or more times more energy efficient than just boiling the salt water.

DC Desalination - The motivation

Tech companies large and small use dozens to hundreds of thousands of processors to make their software work. More and more of these processors are in large data centers (DCs). Of course, large companies have their computers in DCs, but also many small companies are using Amazon’s DCs for their web applications. Moving to datacenters makes financial sense because of economies of scale. One downside of large DCs is that they generate a lot of heat. You can typically measure the size of a datacenter in dozens of megawatts. DCs shed the heat by either dumping it into water bodies (rare) or, more commonly, by using cooling towers like you see for nuclear reactors. All of that heat has value and should be put to use instead of wasted.